In analysis using a liquid chromatograph, an autosampler is used in order to automatically introduce a plurality of samples into an analysis column according to a predetermined sequence. As the autosampler, a full injection type or a partial injection type exists.
In the full injection type autosampler, a predetermined amount of a sample is sucked from a sample container using a needle connected to a syringe pump so that the sample stays inside a sample loop connected to a proximal end of the needle. Subsequently, a needle tip is inserted into an injection port provided as one port of a rotary type high-pressure valve and the high-pressure valve is selected so that a sample loop is interposed between a feeding pump feeding a moving-phase liquid and an analysis flow path communicating with an analysis column. Accordingly, the sample staying in the sample loop is carried by the moving-phase liquid from the feeding pump and is introduced into the analysis column.
In the partial injection type autosampler, a sample is sucked using a needle connected to a syringe pump and the needle is inserted into an injection port provided in a high-pressure valve so that a predetermined amount of the sample is injected into a sample loop of which both ends are connected to ports of the high-pressure valve through the injection port. Then, the high-pressure valve is selected so that the sample loop is interposed between an analysis flow path and a feeding pump feeding a moving-phase liquid. Accordingly, the sample injected into the sample loop is introduced into an analysis column.
In the analysis using the liquid chromatograph, there is known an analysis method called gradient analysis in which two or more kinds of solvents are mixed as a moving-phase liquid and are fed while a mixing concentration ratio is gradually changed (see Patent Document 1). When the gradient analysis is used, an elution time of the sample from the analysis column is controlled to sharpen a peak shape or shorten an analysis time by decreasing the sample elution time.
In the gradient analysis, there are two kinds of analysis including high-pressure gradient analysis and low-pressure gradient analysis. The high-pressure gradient analysis is a type in which one feeding pump is used for one kind of a solvent and a concentration ratio of solvents mixed by a mixer is adjusted in such a manner that flow rates of the liquids fed from the feeding pumps are controlled while a plurality of kinds of solvents are fed to the mixer at the same time. Meanwhile, the low-pressure gradient analysis is to feed a plurality of kinds of solvents by one feeding pump and a concentration ratio of solvents mixed by a mixer is adjusted by a switching timing control for a flow path switching valve provided at a front stage of the mixer. In general, when there is a need to shorten the analysis time, the high-pressure gradient analysis having a “shorter delay capacity” is used.